People already buy it illegally. I don't see how this will meaningfully change the supply or demand.
You should read up on harm reduction.
MDMA very realistically shouldn’t be lumped in with cocaine, heroin, etc. Hell, opiates as a whole! Just based on the effect profile and typical usage patterns, I baselessly posit that one is more likely to be a daily marijuana user than a daily MDMA user, even taking into account the number of people that use each drug in the first place.
Nobody is holding you up with a knife or gun, or stealing the coins out of your car, to get their next fix of MDMA.
Nobody is acting aggressively on the street or in a nightclub because they’ve had MDMA, or not gotten enough of it.
MDMA is certainly not without its risks / dangers. Someone can easily irresponsibly take too much and end up in hospital or dead. Someone can easily take the right amount of the right stuff and end up in hospital or dead just because they had an adverse reaction. You could ruin your relationships, throw your brain off-balance such that you never really enjoy anything again. There’s the whole ‘gateway drug’ argument. Blah blah blah.
Let’s really stop and think very carefully about whether these risks (which unlike say…meth, heroin, etc, have an absolutely negligible societal impact per capita compared to alcohol, tobacco, etc) should even show up on the radar when weighed up against the increasingly proven positive effects of MDMA-assisted psychotherapy.